With a cutting tool requiring abrasion resistance, sliding properties and fracture resistance, there have currently been used techniques of forming a variety of coating layers on the surface of a hard substrate made of WC-based cemented carbide, TiCN-based cermet or the like, to improve the abrasion resistance and the fracture resistance of the cutting tool.
While a TiCN layer or a TiAlN layer have been generally and broadly used as such a coating layer, there have been development of a variety of coating layers with the aim of further improving the abrasion resistance and fracture resistance.
For instance, Patent Document 1 discloses a throwaway insert where a value of a ratio I(200)/I(111) of a diffraction intensity I(200) of a plane (200) to a diffraction intensity I(111) of a plane (111) in X-ray diffraction of a TiAl composite compound layer that coats the surface of the substrate is controlled so as not to be smaller than 1. Further, Patent Document 2 discloses a throwaway insert where a value Ib(220)/Ia(111) of diffraction intensities in X-ray diffraction of a TiAl composite compound layer is set within a range of “1.0<Ib/Ia≦5.0” for enhancing oxidation resistance and flaking resistance of a coating layer.
Moreover, Patent Document 3 describes controlling peak intensity ratios of crystal planes (111), (200) and (220) which are measured in X-ray diffraction on a coating layer made of TiAlCr-based composite nitride or carbonitride. It is to be noted that few diffraction peaks of a plane (400) exist in an X-ray diffraction chart illustrated as FIG. 6 in this document. Furthermore, Patent Document 4 describes formation of a laminated structure of a first layer with a crystal plane (200) having the maximum height and a second layer with a crystal plane (111) having the maximum height in a TiAl nitride layer.
As described in above Patent Documents 1 to 4, it is known that controlling diffraction intensities in X-ray diffraction in the TiAl composite nitride layer to control characteristics of the coating layer, especially controlling the crystal planes (111), (200) and (220) having large diffraction intensities, enhances hardness and oxidation resistance of the coating layer, while also enhancing adhesiveness to the substrate.    Patent Document 1: Japanese Patent Laid Open Publication No. H9-295204    Patent Document 2: Japanese Patent Laid Open Publication No. H9-300106    Patent Document 3: Japanese Patent Laid Open Publication No. 2002-3284    Patent Document 4: Japanese Patent Laid Open Publication No. H10-330914